Well described Dale... Let me add that incidence is a term which applies to both the wing and horizontal stab using the Datum line as a reference point. Some measure the wings incidence and compare it to or against the horizontal stabs.

The Datum line is an imaginary line that is drawn through the fuse length wise. Typically Aerobatic models with a removable canopy deck can utilize this surface as Datum reference point. In some cases the firewall has no up or down thrust and can be used as reference point.

You'd first have know the desired incidence spec for the wing and then the stab. As a general rule Aerobatic models are set at 0 degrees for the wing and stab. Most aerobatic models with plug in wings and stabs are easy to change the incidence on by relocating the ply doubler/socket located on the inside of the fuse which the dowel penetrates into. Or in some case stabs have a small L-bracket that is used to locate the stab's incidence and hold it in place.

I'd suggest Robarts Incidence meter, very good instructions with lot's of examples and how too's, simple and rugged construction.

Great Planes has a very nice Laser unit as well.

ARF's are assembled with jigs, the incidence is set with the jig when the model is framed up, they are generally close enough for the Sunday flier. I'd fly your model and go from there...